Channel extension in telegraph systems



Sept. l0, 1940. R.- E. MATHES CHANNEL EXTENSION IN TELEGRAPH SYSTEMS Filed Nov. 1, 1938 4 Sheets-Sheet 1 ATTORNEY Sept 10, 1940. R. E. MATHEs 2,214,642

CHANNEL EXTENSION IN TELEGRAPH SYSTEMS Filed NGV. l, 1938 4 SheelZS-Sheetl 2 INVENTOR ,4P/(M4199 LSVb/[6' BYv ATTORNEY Sept. 10, 1940. R. E. MATHl-:s

CHANNEL EXTENSION IN TELEGRAPH SYSTEMS Filed Nov. 1, 1938 4 Sheets-Sheet 5 l SNC. .aka

ATTORNEY Sept. l0, 1940.' R, E, MA1-HES 2,214,642

CHANNEL EXTENSION IN TELEGRAPH SYSTEMS Filed Nov. 1, 193e 4 sheetssheet 4 E' Ll. y; L

H 'l E, J l# Jg F, J Jg E. J h, L H |-I E, 11 ,d l?

JL #i s 1 3u [u -JL 151 H JJ E k, Jg# H `t| H E 1S"L\ E ,q L H j Ei H 'n jb- E w'l 1 1 'IHH) 'rlmlvlsf4 INVENToR 2Mb/HPD E. BY 7% ww ATTORNEY Patented Sept. 10, 1940 CHANNEL EXTENSION 1N TELEGRAPH y SYSTEMS Richard E. Mathesiwestneia, N. J., assigner to Radio Corporation of America, a, corporation of Delaware Application November 1, 1938, Serial No. 238,168

' .This invention relates to channel extension in multiplex telegraph systems in which signals are relayed automatically from one station to another through still another station. Such channel extension is desirable in radio circuits because of atmospheric conditions or because of the desire to use the more powerful or more directional system of the station through which the channel is automatically extended. Channel extension is also more economical both in wave bands and in equipment used in the communication system. In wire line telegraphy such extension is often desirable or necessary because of storms, floods y or other catastrophes that may interrupt or cripple direct service between two stations, while service between a third station and each of said two stations remains unaffected.

The invention is useful in both radio and wire systems but byway of example, it has been illus-i 18 Claims.

trated in connection with radio systems.

An object of the invention is to relay or extend the channel from a branch or controlled station, through the main or control station, to another branch station with minimum change'of equipment already installed for direct communication between the stations.

Another object is to maintain in synchronism two mechanically separate channel-selecting means by driving one selecting means by alternating ory pulsating current generated by the other selecting means.

Another object of the invention is to drive the transmitting selector or kicker of a station by' a synchronous motor obtaining-its operating current from an alternating or pulsating, current generator driven by the kicker of the receiver at such station.

which Fig. 1 is a symbolic representation of a main station and two branch stations.

Fig. 2 is a part symbolic and a part circuit arrangement of the receiver and transmitter of a station such as B and C.

Fig. 3 is a part symbolic and par-t circuit arrangement of a station such as A.

system.

In multiplex systems, the wire transmission line in wire telegraphy or the radio equipment in radio telegraphy is assigned in rapid succession to a number of keying or' receiving channels. The number of channels thus combined may 5- number from two upwards. In radio circuits it has been found that the combining of three channels makes a very satisfactory system and in explaining my inventionv a three channel system will be assumed, though obviously more or less 101 channels may be used.

Multiplex systems of various numbers of channels are well known in the art, asy shown for example, in my Patent No. 1,979,484, of November 6, 1934. Expedients for keeping the receiving distributor in synchronism with the transmitter distributors are also known in the art. For a detailed description vof a suitable arrangement I refer to my Patent No. 2,038,375, dated April 21,v

1936. Various other well known devices will be Y necessarily referred to in explaining the operation of my invention. To fully illustrate and completely explain all these well known devices would needlessly expand the disclosure. I therefore will illustrate and describe in detail only such prior art devices and methods as Will be necessary to a full understanding of the invention.

In multiplex Systems where there is only direct communication between the main or control station and the branch or controlled stations, it is only necessary for the main station to con-- trol the speed of the receiving distributors at the branch stations and vice versa, but to successfully carry out automatic channel extension in such system, it is necessary for the control or relay station to control also the speed ofv the transmitting distributor at the controlled or relaying stations.

To aid in understanding the problem and therefore applicants solution in channel extension, let it be assumed thata transmitting station in New York has facilities for communicating with a station in Chicago and another station in San Francisco. this New York station will have a transmitter and a receiver for Chicago communication and another transmitter and receiver for San Francisco communication. The Chicago station will likewise have a transmitter and a receiver reserved for the New York station and an additional transmitter and receiver for the San Francisco station. San Francisco will be similarly equipped with a pair of units for New York communication and another pair for Chicago 55,y

It will also be assumed-that l communication. With this prior art construction the New York transmitter would cause its Chicago receiver to operate in absolute synchronism or at a constant proportional speed with its own transmitting distributor (Mathes Patent 2,028,375). This would be accomplished by the standard frequency unit and the speed correction unit later described-herein. Similarly the Chicago transmitter, reserved for New York communication, would control the speed of the distributor of its receiving station a-t New York. The transmitters and receivers of the other communication circuits referred to would be similarly tied up. In each case the transmitter controls the distributor speed of its distant 1eceiver. All of the transmitter distributors would operate approximately at the same speed only. This prior art circuit is entirely satisfactory as long as there is no attempt to relay messages through another station by channel extension. It makes no difference to New York in direct communication that its Chicago receiving distributor is out of step with its Chicago transmitter. If atmospheric or other conditions makes it inadvlsable to communicate, say from Chicago to San Francisco, and there is good communication conditions between Chicago andNew York, and betweenNew York and San Francisco, Chicago will relay its San Francisco communication through thel New York station. Under such conditions it is absolutely necessary that the New York receiver, reserved for Chicago communication, be running in synchronism or at a constant proportional speed in respect to the transmitterat New York which is to relay the communication von to r'San Francisco.

c Itis also necessary at the relay station, lNew York inthe example given, to adjust the phase of the communication coming in from Chicago so that it will t. in with `the other channels that are Sending communications to San Francisco through the same distributor.

` There has been an attempt to overcomethe foregoing Vdisadvantage so that kcommunication can be automatically relayed from one station to another in multiplex systems, but as lfar as I am aware,`inv such systems this has been done by mounting the receiving and transmitting distributors on a common shaft. While this secures the desired control, it greatly reduces the iiexibfility of the system and in addition requires major and expensive mechanical yand electrical changes to be made in existing systems where thev distributors are separate and sometimes widely separated from each other. Another disadvantage of'fsuch a channel extension system is that the inbound system fails whenever the outbound system fails. In 'such case this shuts down not only the relaying system but also the direct station-to-station communication. In my invention these difficulties are overcome.

In Fig. l, I have shown a channel extension system in more or less symbolic form to illustrate the general operation of my improvement. The main or control station A located, for eX- ample, `at New York city, has a transmitter 'l and receiver 2 for direct communication with the the receiver 3'and transmitter d of a branch sta-r tion'B located at Chicago', for example. The main station A, also has a transmitter 5 and a receiver for communicating with the receiver 'l and transmitter 8 of branch station C located, for example, at San Francisco. This is illustrative only,v as various other branch stations in this or foreign countries could have similar consired output.

nections with the main station and any of the branch stations could be equipped for extending their channels through the main station.

Fig. 2 illustrates in considerably more detail the apparatus used in the stations. At the branch stations it is essential that the transmitting distributor 9 and the receiving distributor I0 run at synchronism for channel extension. To accomplish this, `I install on the driving shaft of the receiving distributor a toothed Wheel il of magnetic material so as to rotate in unison therewith. Adjacent to the 'periphery of this toothed wheel is la solenoid I2 having vpreferably an iron core with a small air gapbetween Such @ore and. the teeth of the when.

This 'solenoid may be energized by any suitable source such as the "battery i3 and it may be connected to an amplifier ,i4 to produce the de- The distributor shaft of the receiver is run by a synchronous motor i5 taking its driving current from aThyra'tron inverter power-unit i6 whose frequency is. setv by the standard frequency unit Il either at the-frequency of the standar-d or any sub-multiple thereof. This standard frequency unit may be of the well known type controlled by a tuning fork and having temperature regulation to maintain a standard frequency to within one part in 100,000 over a long period of time. Such a constant frequency unit is described in an article written by me jointly with J. L. Callahan and A. Kahn, in the Proceedings of the Institute of Radio Engineers, January, 1938, volume26,l

No. 1, page 7l. The standard. frequency units at the branch stations B and C are exactlyv the same as the standard frequency unitY of transmitting station A.

Inverter power units are ,well known, being fully described in the literature, for` example, on pages 231 to 242, inclusive, ofr a .book entitled Electron Tubes in Industry, b-y Keith .I-Ienney, published by McGraw Hill Book Company, 1937 edition. units to facsimile telegraph systems is also disclosed in the patent to'C. J. Young, No. 2,117,587, May 17, 1938. It therefore will be unnecessary to describe the details of the inverterunit I6 herein. It .will be sufficient to say` that thev to maintain a source of voltage of the same fre;-l

quency or any harmonic or sub-harmonicthereof, at any desired higher power.

glow tubes. l e Since the voltage of the inverter unit vviii'is applied to the synchronous motors I5, `thedis.-` tributor shaft and the toothed wheel Il will'run` synchronously with the frequency of the inverter which has either the frequency of the standard frequency unit or any selected multiple or submultiple thereof, depending upon its adjustment.

Also, since the same standard frequency unit. is

being operated at the control station A, alljthe motors l5 will runy in practical synchronism `with 'Ihe application of inverter power- Y Thegas tubes. are` frequently called Ifhyratronsf` orv Grid the desired frequency unit 'of the main or control station. However, it is practically impossithe' frequencies of thestandard'units; the speeds ofthe distributor shafts at the branch stations are I'corrected' to absolute synchronism by the vcorrection unit 'I8 and a correction motor 'I9 geared to the frame,or stator, as it is'. usually called, .of the synchronous motor I5. l' f.

The Standard frequency units, distributors and .other parts vreferred to herein of course 'need not be run at one and thensame speed. l'Ihe'units and devices may. operate at different frequency or speed and the principle of the invention may be used so long as such frequencies or. speeds bear a constant ratio to each other.

In general, the-speed is corrected to maintain absolute synchronism between the distributor shaft of the receiver of a branch station with the distributor of .the transmitter at the control station by means of the signals themselves. These signals, of course, are in absolute synchronism at all times with the transmitter sending out such signals though there maybe, and in nearly al1.- cases is, a slight shift in phase. This speed correction unit is well known in the art, being described in my above mentioned Patent No. 2,038,375. It may be said, however, that in this speed controlsystem the distributors of the receivers are run by synchronous motors that are energized by alternating current generators (gas tube inverters beingv disclosed), controlled by the standard frequency units. Standard frequency units are tuning-fork controlled and they are set so that they operate at frequencies towithin one part in 100,000 of each other. This-minute difference in frequency would soon throw the transmitter and receiver distributors out of step an-d to keep them absolutely in synchronism, or at speeds bearing a constant ratio to each other, a pulsating current is generated by the dot'and dash signals arriving vat the receiver from the distant transmitter. Afportion'of the signal energy arriving at the receiver'is passed through a transformer which generates a pulse at thebeginning and also at the end of each dot or dash. One of these is suppressed, say the terminal pulse, and the other one is used to energize arelay to place voltage of .one polarity .on a field of a motor that rotatesl the stator of the synchronous motor in one direction when the receiving distributor is operating fast.w.:.'I`hisl pulse'whenv the distributor is running slow energizes the re- I lay to apply voltage of opposite polarity, to the speed correction motor which kicks the stator of the synchronous motor in the opposite direction. Aslong as the receiving distributor isI operating Ain step with the transmitting distributor thecirtiple or harmonicfrequency since the desired frequencyfor the transmitter distributor can be obtained by adjustment of the inverter. If the standard frequencyx units IIjv are maintaining substantially a frequency of 480 cycles per second, and the synchronous motors I5 arev connected to operate` on the eighth sub-harmonic, yor 60 cycles, from the output off the inverters I6,then

the speed correction Aunit will run the motor frame of the synchronous motor I5 at the branch Stations4 B and VC either forwards or backwards toi'increase or decrease the speed to maintain the distributors!) and IU in absolute synchronism with the distributor 20 of the control station A.. i

The distributors ZI and 22 of the two receiving stations at control station A are likewise run by synchronous lmotors Isupplied with power from the local inverter power units I6 Whose frequency is set by the standard frequency unit I1 of' station A. The speed of each of these distributors at 'station A is likewise corrected by speed-correction motor I9 to maintain the distributors in synchronism with the `transmitter* distributor of station B or station C and in constant phaserelation therewith. The distributors 9 of the transmitters when no channel extension is made are operated by inverters 2'I, already described, such inverters having their frequencyset 'by the standard frequency unit, switches"23 being then closedl on contacts 24. If thefstandard frequency units at stations B and C. should be slightly out of synchronsm with standard frequency unit I'I of station A, the speed correction units I8 at station A willmainltain the receiving distributors 2| and I22 in synchronism with the transmitter shaft at stations B and C.

The speed. controls Vas already described are ample for taking care of Vdirect communication between stations A and. B, and between stations A and C. However, as will be appreciated, the

speed correction units do not maintain the receiving distributors 2l :and 22 at station A in absolute synchronism with the transmitting distributor shafts 20 at station A. 'The speeds of these receiving distributors at station A will differ fromY the speed of the transmitting distributors at the same station by the amount that the standard frequency units II at station B or. C depart from the frequency of unit I'I at station A. Thusywith the regular equipment already described, it would beimpracticable to relayy communication' from one branch station to-th-e other branch stations through the control station A.

By throwing switches 23 at the branch stations soas to engage contacts. 25, the' solenoid I2 is -able tocontrol the frequency applied to the synchronous motors 26 operatingthe .distributors 9. If it be assumed that the inverters are so adjusted that all stations are'operating on theeighth sub-multiple of the standard 480 frequency ofthe units I'I, or 60 cycles, and that the toothed wheels II at stations B and C have IS teeth, there will be generatedin the solenoids I2 `a frequency ofl 480 cycles, the synchronous motors I 5 having four poles. If a standard frequency unit II at station A varies a light amountfrom 480 cycles per second, the frequency produced by the'tone wheel II and solenoid I2- will vary Vexactly by the same amount because. the speed correction unit I9 is maintaining the distributor shaft in exact synchronism with the frequency unit at station` A. The insverterpower units 21 thus'. produce a fre- .quency inexact synchronismor a sub-multiple close of each dot or dash the switches are thrown multiple of 480 cycles the synchronous motor 25 and the transmitting distributors 9 at stationsB and C will be operated on 60 cycles "and will be in synchronism with the transmitting ldistributors 25 at station A though not necessarily in exact phase y 1 With this explanation, let it be assumed that station B is communicating with station C on channel I by relaying .such communication through station A, and that channels II and III of stations A and C and A and B are being used in direct communication.

Referring particularly to Fig.y 2 for more detailed explanation of stations C and B, the messages in channels I, II and III will be sent out by telegraphic tape transmitter heads. These headsrare run by synchronous motors 3| fed with alternating current from inverter 21 at the desired frequency. They, therefore, are run synchronously with the transmitter distributor arm 39. These heads are well 'known in the art and need not be described further than to say that perforated tape is fed through the heads bythe mechanism and at the beginning of each dot or dash, the switch members 32 `are thrown into engagement with the positive terminal of some source such as the battery 33. At the into engagement with the negative terminal of the battery 33.

The rsignal that is to be relayed through station A to station C by assumption will be sent through channel I but the progress of all three signalswill be traced from station B to station A. The impulses sent out by the keyers will g-o over transmission lines 34 to the cont-acts on'the distributor. The signals being sent out by extended channel I and direct channels II and III are given yat Ia, IIct and IIIa in Fig. 4. These three graphs give the full dots, dashes and spaces of the Morse code in a portion of the message. When the distributor arm engages contact 35 a pulse of current 40 (graph Ib, Fig.r 4) will pass from channel I through contact`35, distributor arm 39, to collector brush 4| and to the grid of vacuum tube 42 of the locking cir-l cuit tone keyer. Toothedclutches 40 between the synchronous motors and the transmitting heads permit one to adjust these heads in respect to the position of the arm 39 and thus assure that the contacts will be made at the center of each baud. The current through brush 4l continues to flow only so longv as the distributor arm is in engagement with contact 35. In practice this pulse of current 4t! will be much less than theV length of a baud'depending upon the width of the contacts, the width of the brush and the spacing between the contacts. A pulse of about 1/10 to 2%() of a baud will be found suitable.

The pulse of current reaching the grid of tube 42 applies a positive potential thereto which sends current through resistance 43 to the negative terminal of the battery. Before this pulse was applied the locking unit was in unstable condition because of the interconnection of the grids to the plate circuits as explained in the patent of J'. L. Finch, No; 1,844,950, February 16, 1932.

Before the pulse was applied to the grid of tube 42 current from the positive terminal of the locking unit came in through connection 44 where it divided and passed in two diierent branches, one being through resistance 45, resistance 45, resistance 4I, to the negative terminal. vThe current in the other branch passed sistances.

through resistance 48, resistance y49 and resistance 43,` to the negative terminal. The drop in these various resistancesmight place both grids just above the cut-oif'point or just below it, depending upon the chosen Values of the re- In either case this is an unstable arrangement and either one tubey [or the other is certain to take slightly more plate current,`

forv example, tube I, and this will draw increased current from the positive terminal 44 through resistance-48 to the plate and filament 50 yof the tube and to ground lwhich is connected to the intermediate terminal of the battery. This decreases the potential at the junction point 52 andcorrespondingly lowers the potential at junction point 53. Since this' latter junction pointis connected to the grid of tube 42, this grid goes more negative and the tube draws less current. This decreases the load current through resistance 45 and raises the potential of junction point 54 by decreasing the drop in resistance i5 and this lowers further still the potential on the grid of tube d2 due to increased current in the plate circuit of tube 5l. The net result is that the tubes in the locking arrange'- ment, when no signal pulse is being received,

are so unstable that either one tube or the other is always drawing current and the other one is blocking.

By assumption, tube 5l is drawing current and tube 4,2 is blocking at the vtime that the positive puls-e 4D (graph Iby of Fig. 4)` is applied to the grid` of tube 42. The positive pulse 43 applied the grid of tube 42 and it starts drawing current. grids this will cause tube 5I to instantly block. When contact arm 39 leaves contact 35, pulse 40 terminates. Nevertheless, current-still continues to flow through the tube 42 because of the locking arrangement already explained. A posiat the junction point 53 raises the potential of Because of the cross connection of the tive potential is appliedthrough the conductor 55 to the grid of push pull tube 55 in the tone keyer arrangement. This causes push pull tubes 56 and. 5'I.to draw current in push pullv fashion and current will continue to flow froml the time pulse 40 was applied to the grid until the bal'- ance of the locking arrangement is upset. Tone generator 58 therefore will send a tone modulated current through transformerv 59 and transmission line 33 to the transmitter 6i and radiation Will commence.

When the contact arm 39 engages contact 36 of channel II, positive pulse 62 (graph IIb) will be applied to the grid at point 53. This itself would have been sumcient'to causetube 42 to.

draw current, but since it isr already drawing current bymeans of the locking arrangement it has no effect. .The contact arm 39 next engagesy contactl 3l and sends out positive pulse 63k (graph IIIb) from. channel III. This likewise has no eiect on tube 42 as-it isI already drawing current.

When the Contact arm again swings on to Contact 35, positive pulse 54 will be sent out from extended channel I. This likewise will cause no change in the locking circuit. When Ythe contact arm reaches contact 36,' negative pulse G5 (graph IIb) will be sent out because,u

5| instantly .draws 'current through the unsta.- 75

^ composite signal radiated vby the antenna.

ble fequilibriumproducedubyf'the cross connection'of the grids.- tial to be applied tothe grid of push pull tubes 56 and 51. These tubes then block and no signal issent out bytransmitter 6I. This terminates thev composite signal character 66 (graph V). x

- When the contact arm, reaches contact V31 neg'- ative pulse 66"'from channel III'will be produced but this'has no effect as tube42 is alreadyv block-ed. When the contact arm reaches contact 35 a positive potential is still beingA applied -to channel I, as l.shown by graph Ia.l A positive pulse 61 is therefore applied to junction point 53.

This instantly causes tube 42 to draw current and tube I to block. This terminates the composite space character 58 (graph V) of the composite signal being sent out by thetransmitter 5 l.

The point atwhich transmitting channels I, II and III are connected by contacts 35, 36 and 31 to the locking unit can rbe readily determined by inspection of the group I of graphs in Fig. 4. The positions of lchannels I, II and III at the top of this group indicate the moment that contact is made between the distributor arm and each of thel three contacts. -The vertical lines proceeding from these Roman numerals indicate whether a positive or a negative pulse is transmitted to the grid of tube 42. To determine this one has merely to note Where the lines from I, II and III cross the graphs Ib, IIband IIIb, respectively.' i

It Will be seen Without further detailed description that the distributor arm and locking arrangement will combine the signals into ka composite arrangement shown by graphs IV, V, which will be unintelligible vto an unauthorized listener. Graph IV is the composite signal reaching the tone keyers and graph V is th-e At the receiving station A, Figs. l and 3, the signals will be received on the antenna of receiver 2 and Will'be fed into the distributor 2l. The signal received will take. the form shown in graph VI of Fig; 4. vThis will, be thesame as graph V. signals are shown. The Roman numerals at the top of this group show the times of closure of the contacts on'the receiving distributor of station A. As will be noted, these contacts are closed a half baud laterthanthe-closure at thetransmitter distributor station C' because of the desire to have these closures made at the center o the bauds of graph VII. 1

The received signal will be tone-keyed, ampliiied and rectied, after which it will appear as a pulsating current, as shown by graph VII. The locking unit 10 of the 4receiving vapparatus at station A is like the one-described in connection with the transmission from station B but since rectified current, in which the potentialschange from positive to zero and vice versa, is applied to the locking unit instead of alternating cur'- rent, in which the potentials change from positive to Zero and vice versa.l I use :a coupling tube 1l before the signal reaches the locking unit and a condenser 12 between the distributor and the locking unit 10. Battery 13 .biases the grid of tube 1l positive so that it normally conducts current through resistance 14.

When contact 15 engages contact 16, point 66 under Roman numeral I thereabove of graph VII shows that a positive potential exists at double rectifier 11 across ground'terminal 18 and cen- 715; ter .tapj19,. thenterminal` 18` beingv positive and This causes a negative poten-,`

In the graphs of lgroup B the receiving the-center.; tap 19 being negative. This biases the gridof tube 1| so strongly negative that it 'blocks Therei'beingwno plate current through resistance 14, practically the full voltage of the batt-ery is applied through contact 15 to the condenser 12 and grid resistance 80. :Resistance 89 is high in comparison to resistance 14 so that the charging or displacement current of cone denser 12 produces a sufficient positive drop around the former to cause the tube 8l tor draw current and tube 82 to block. Channels II and III ywould have a locking unit and condenser connected to contacts'83 and 84, respectively, but'the operation will be vunderstood with only one locking arrangement being shown.

`Wherrthe tube 8| began to draw current,l current started to flow from conductor 85 through resistance 89 to the plate of the tube and thence` to the filament and to ground. `Since tube 82 is blocked no plate current owsthrough re' sistance 81. The phasing delaydevice 88 is con-v nected across resistance 86 and 81 by conductors 89 and gli. When tube-8l is drawing current con- ,ductor 90 is positive and conductor 89 negative.

When tube 8l blocks'and tube 82 draws current, tne'polarity of conductors 89and 90 is reversed. BeIore explaining the phasing or delay action the reformation ofhthe signals of all three channelswilly be traced. A

When tube 8l ,draws current dash 9| (graph Ic) starts to form andthis dash willcontinue dueV toA the action of the locking unit untila much diminished potential is placed on the grid of tube 3l. rBy inspection of graph VIIgit will be clear that there is no change in potential except between points 92vand 93. This cannot affect locking tube^8l,z'however, becauseA the distributor arm 15 is not in engagement with contact 16 of channel -I during the space between points 92 and-93, aswill be clear by referring tothe Roman numerals at rthe top of Fig. 4.

The next "change :in potential occurs between the points 94 vand 95 orgraph VII. By referring to thefRoman numerals at the top of Fig.

4, Tit Will'beseen that contact 15 engages contact 1S of channel I at thepoint 94'. Conseuently,l the kdash in channel I (graph Ic) terminates at 96 and the .space 91 starts to form. When point. 94 was reached in the composite signal the rectiiier 19 produced no current. This meant that the negative bias was removed from the grid of tube 1l and it drew current due tov the positive ybias `oiy battery 13. This produced a drop vin load resistance 14 of'tube 1| and the voltage applied to condenser 12 :was `decreasedy by the amount 'of the drop therein. Condenser 1 therefore discharged and placed a momentary bias on the grid of tube 8l due to the drop in resistance 'produced by the. discharge current.A This discharge'took place through the distributor-arm, to the plate oi tube 1l and thence to the iilamentv and tothe negative terminal of the battery through groundl and thence through resistance 8U to theother side of condenser 12. I f

The negative charge on the grid ofthe tube 8l caused the tube to instantlyblock and tube B2 to draw current. This caused current from the positive terminal to flowthrough conductor 35 and resistance B1 and thence through the plate-filament circuit `of tube T82. This oW of current produced a drop in resistance81 that made conductor 9D negative and conductor 89 positive. This reversal of current acted on the phasing delay unit but before describing that The space 97 continues until there vis another change of potential. applied to condenser '12. On inspection of graph VII in connection with the vertical lines connected tothe Roman numerals at the top of the graphs of group B,

`Fig. 3, it will be seen that channel I cannot be affected until the point 98 is reached. At noY place between points 94 and 98 of this graph is contact arm 'l5 in engagement with contact I6 of channel I. However, at point 98, arm l5 does make engagement with contact 16 and the grid of tube 8| grows strongly positive due to the action of the rectifier 11 and coupling tube 1| already explained. The dash of channel Iv thus commences to form at the point 98 and it cannot be interrupted until there is an interruption of the current at the time that arm 'l5 reaches contact 16. By an inspection of graph VII it is seen that the rst interruption of the current is between points 99 and |00. By tracing the vertical lines from these points to the Roman numerals at the top of the graphs V of group R, it will be seen that channel I is not affected at this time. Therefore, the dash starting at 98 continues until point |012 is reached on the composite signal shown in graph VII. By following the vertical line from point |02 tothe topv of the group of graphs it is seen that channel I is affected because arm 'I5 is in` engagement with contact 16. No

Tl to place a negative bias on tube 1|. denser 'l2 therefore discharges again and places a negative bias on the grid of tube 8| and the tube instantly blocks. This reverses the polarity of conductors 89 and 90 again and the dash begun at point 98' of graph Ic ends at |02. By

referring to graph Ia-of group I of Fig. 4 of` the original signal in channel I, it will be seen that graph Ic is exactly the same as graph Ia except that it has been relayed one full baud in time due to the fact that the signal was delayed a half baud by being picked 01T in the middle of the baud at the transmitter and againv a half baud at the receiver for the same reason.

Channels II and III would be connected to a condenser and locking arrangement like those of channel I in Fig. 2. -In channel II the signal starts -to form at point |03 of graph IIa.

By inspection of the composite signals shown in graph VII, it will be seen that there is no change of potential until the point 92 is reached and by following the vertical line upwards to the top of Fig. 4 itis at once seen that this is applied to contact 83 of channel 1I at the point |04. This terminates the character at point |04 in graph IIc and a space then starts to form which continues until the neXt change of potential affecting channel II occurs. By inspectionof graph VII it is seen that this change of potential does not occur until point |05 of the composite signal is reached. The vertical line through this point shows that channel II isaffected and the space terminates atv |09 (graph IIc). Another signal character then starts to form. This will continue until there is another change of potential affecting channel II. It-will be seen from an inspection of graph VII that the potential does not change until point 99 is reached in that graph. Here the potential drops one-half baud before contacts 'l5 and 83 are in engagement. 'I'he signal channel in channel II therefore terminates at current, therefore, flows at this time through rectifier` Con-v 01 (graph IIc). This starts the formation of a space and the space will continue until there isa change in potential while contact 'I5 engages contact 83. This does notoccur until point |09 Yof graph VII is reached. At this time` anew character starts at point |09 (graph IIe). This continues until the potential is again changed while arm 75 is inengagement with contact 03. This does not happen until point H0 is reached in graph VI. The signal char. acter, therefore, ends at point By comparing the graph IIC, group'R, with the original of graph IIa, group T, it will be seen that they are exactly kthe same but the signal starts later by two bauds.

In ychannel III the `'signal character starts forming at ||2. At point H3 of graph VII', switchV arm 'l5 is in` engagement with contact 84. Sinceat this time graph VII shows that no current is flowing, the signal character will terminate at H4. The space will continue until the potential changes. At point H6 the arm rtf and contact of channel III are together again and at this point there is a potential increase so another signal in channel III will start at H6. This continues until the next engagement of the contacts which occurs at (graph VII).r

Since the potential drops at this point the signal in graph IIIc terminates at H8. A space then starts to form. The contacts of channel III are next in engagement at point I9 of graph VII. Since there is current flowing at this point a new'signal in graph IIIc. starts at |20. YThe contacts in channel III' are next in engagement at |2l. At this time positive potential also exists. Therefore, the signal character continues At point |22 the contacts ofv n without change. channel III `are again in engagement. At this time graph VI shows that positive potential eX- ists. Therefore, the signal character started at |26 of graph IIIe still continues. The contacts are next in engagement at point |23. Graph VII shows that at this timeV no'current is flowing and therefore the signal character in channel IIIc ends at |24. `By comparing reconstructed signals of channel III in IIIc with Vthe original signals of this channel in graph IIIa, it will be be seen that the two are identical except that the former has vbeen delayed in` phase one and one-half bauds. l'

Since receiving channels II' and III,` by assumption, terminated' at station A, there is nothing further to `explain in connection with these two channels except'to say that they would be connected to locking circuits similar to 'l0 and to recording or other receiving devices which are well known in. the art andare not shown. Channel I, however, by assumption, is to be relayed at station A, to station C. Therefore, the signal of graph Ic will be traced further..

As previously explained, and as shown in Fig. 3, this signal has been placed by the conductors 89 and 99 on the phase delay unit 88 so that ad justment can be made to provide for the taking of the signal at approximately the center part of the baud.

Phase delay eXpedients are well known in the art. 'Combinations of resistance and capacityA as well as resistance and induct'ance will provide for easy shift of phase. Also magnetic storing devices for shifting the phase may be used and I `have shown the latter type merely by way of stored on magnetic material, except for phase shift variation, as in my invention,the` pick-up should be adjustable. In the device shown in Fig. 3 a disc |25 of magnetic material of suitable magnetic permanency is rotated by any constant speed motor |26. This may be a .clockwork mechanism or any type of electric motor adapted to maintain a constant speed.

Magnet |21 places a magnetic bias on the disc |25, one side being a north poleand the other sidel a south pole. Electromagnet |28 superimposes a magnetization from -the lsignals on this disc and pick-up magnety |29 has a variable current generated by the variable magnetization placed on the disc by magnet |28. The pickup magnet |29 is adjustable around the disc, towards or from the magnet |28, as indicated by the double arrow |30. Magnet |21 then Wipes off the magnetization placed on the disc by the `electromagnet |28` and restores the magnetic bias. f

When the signals received over channel I reverse the polarity 'of conductors'BB and 90, as already explained, the polarity of.' magnet |28 reverses and it places" a corresponding magnetization on the disc |25. As the disc rotates this magnetization produces a pulse of current inthe pick-up magnet |29. By adjustingy thev pick-up magnet |29 towards or fromV magnet |28 4the phase of the signal pulses in magnet |29 can be readily adjusted in respect to the signal currents in magnet |28. By the magnetic phase shifter the phase can be delayed'so that the distributor arm of the transmitter 20 at station A can pick offv the signals at the center of a baud. I his can be readily done by a stroboscope Vsuch as neon lamp |32 connected by brushes and lines4 |34 with the potentiometer |35 that carries the signal currents. The lamp |32 andthe perforated disc |36 rotate in synchronism with the ltransmitting l distributor 20 and -themfla'shing yof the light through the perforation 31 will give the posiq tion of the signal characters inA respect to4 the contact |33. Ihis stroboscopic indicator is not part of my invention and 'it Aneed not be further described since it is known in the art and its operation will be robviou's.

After passing through the phasel shifter the signals are preferably sent 'again through alocking circuit |38 like the transmitter lockingv circuit of Fig. 2 so that they will have a square'form more suitable for combining with'the localsignals in transmitter' channels II` and III which likewise come through similar locking circuits (not indicated). After passing through the distributor 20,' the composite signals pass into4 the locking circuits and tonek keyer |39 `like those of 1,12%. 2, and thence to the transmitting apparatus The radiated signal is received at station C and regenerated as already explained in connecnection with station A and this need not again be explained. v

It will be clear that additional'channels of station C can likewise be extended to station B by way of station A. This'can be taken care of by appropriate' switches, not shown.

l It will be apparent that lsignals can rbe extended through two-'or more relayingv stationsl to another station instead of only one as I have described by way of example.y Also, it will be clear that the main station need not be the relaying station when lthe .other stations are equipped with my improvement. If station B is communicating directly with station C then Istaway multiplex telegraphy between two stations through the same relaying station and the speed of the distributors in communicating in one directionmay be the same as, or different from, the speed of the distributors in the other direction.

Instead ofthe toothed wheel and solenoid, I may use any othertype of synchronous generator for fixing the speed of the distributors at the branch stations so that the channels may be extended through the controlling station A. Also, the generators need not be secured directly on the shaft of the distributors as they may be geared or otherwise connected to generate currents of synchronous frequency or proportional frequency such as sub-multiples of the synchronous frequency. v i

Various phase shifting ordelaying devices may be used in the place of the one illustrated. For example, I may use the one described in the ap'- plication of Alfred Kahn, filed Nov. l, 1938, Serial No. 238,167, assigned to the assignee of my application.

Whilev I have shown a particular form of connecting means for maintaining the distributors of the various branch or controlled stations in synchronism with the distributor of the main or control station, it must be understood that other kinds of connecting means may be used. Also various other'changes may be made in the system described without departing from the spirit of the invention.

Having described my invention, what `I claim 1. In a multiplex telegraph system, a telegraph station having a'tr'ansmitter and a receiver, means for connecting a plurality of receiving channels in succession to the receiver, a generator operated by said means for producing alternating potentials of a frequency proportional lto the rate of connection of said channels and means for connecting a-plurality of transmitting channels to the transmitter under the control of said alternating potentials and at a rate proportional to the frequency thereof.

2. In a multiplex telegraph system, a telegraph station having a transmitter and a receiver, a distributor for each transmitter and receiver, means for running the receiver distributor, at a predetermined speed, a generator of alternating potentials operated by the receiving distributor to run `at a proportionate speed, and means electrically connected to said generator for running said transmitter distributor at a speed yproportional to the frequency of said alternating -the receiving distributor to runat a speed proportional to the speed thereof, a synchronous motor-for running the transmitting distributorand thereto, a synchronous motor connected to run l the transmitting distributors of said one station,

and `means at the other of said stations for adjusting the phase of the signals received from said one station.

5. In a multiplex telegraph system, a control station and a controlled station, each having a transmitter and a receiver, connections for a plurality of signall channels for the transmitter and for the receiver ofsaid stations, means for connecting the. transmitterof the control station to each of its channels-in continuous succession at a constant rate, means for connecting the receiver of the controlled station to each of its respective channels in continuous succession at a rate in synchronism with the rate of connection at the control transmitter, an alternating current generator driven With the connectingr means for the receiver ofthe controlled station at a speed proportional `to the frequency of said rate of connection, and means for connecting the transmitter of the controlled' station'to each of its respective channels in `continuous-succession, said last mentioned means being driven by a synchronous motor'operated under synchronous control from the said generator.

l 6. In a multiplex telegraph system, a control station and a controlled station, each of said Stations having a transmitter anda receiver, a plurality of signal channels for the trnsmitter and for the receiver of said station, means for connecting the transmitter of the control station n to each of its channels in continuous succession at a constant rate, means vforconnecting the receiver ofthe controlled stationy to each of its respective channels in continuous succession at a rate in synchronism WithA the rate of connection at the control transmitter and in phase therewith, an alternating current generator having a frequency proportional to the rate of connectionof the receiver of the controlled station, means for connecting the transmitter of the controlled station to each of its respective channels in succession, said last mentioned-means being operated from the generatorof its respectivereceiver at a frequency proportional to the frequency of the generator, and means for connecting the receiver at the control station to each of its respective channels in succession and lin synchronism with the connecting means of the transmitter of the controlled station. l

7. In a multiplex system having a control station and a plurality of controlled stations, each of said stations having a transmitter and a receiver, a plurality of signal channels for thetransmitter and for the receiver of each station, means for connecting` the transmitter of the control station to each of its respective channels in continuous timed succession at the same and substantially constant rate, means for connecting the receiver' of eachcontrolled station to each of its respective channels in'continuoussuccession at a rate in substantialfsynchronism with the rate of connection of the connecting means of the control transmitters and in phase therewith,

an'alternating currenty generator driven with the connecting means for the receiver of each controlled station at a frequency proportional to the rate of connection, means ,for connecting the transmitter of each controlled station to each ofits respective `channels in succession, said last mentioned means being operated from the generator of its respective receiver at a frequency proportionalA tok the frequency of the generator, means for connecting thereceiver at the control station to each of its respective channels in succession in synchronism with the connecting means of the last mentioned transmitter and means in circuit With at least one of the last mentioned channels to delay for a desired interval of time the transference of signal characters therethrough. y y

8. A multiplex telegraph'system having a control station and a plurality of controlled stations, each of said controlled stations having a transmitter and a receiver and said control station vhaving separate transmitters and receivers for communication with each controlled station, a plurality-of signal channels `for the transmitter and for the receiver of each station, means for connecting the transmitters ofthe control stationto each of their respectiveychannels in continuous succession atr the same'and substantially constant rate, means forconnecting the receiver of' eachcontrolled station -to each of its respective channelsin continuous succession at a rate in substantial synchronism ywith the rate of connection of the connecting means of the control transmitters, and in phase therewith an alternating current generator driven with the connecting means for the receiver of one of the controlled stations and having a frequency proportional to its rate of connectiona synchronous motor for 'connecting the transmitter of feach controlled station to each of its respective channels in succession, said last mentioned means being operated from the generator of its receiver and ata frequency proportional thereto, means for con"- necting one ofthe receivers at the control station .to each of its respective channels in succes-H sion and in synchronism-'with the connecting means of the transmitter of one of the controlled stations, at least one of the last mentioned channels havingk an electrical connection with the channels'of one oi? the transmitters of the control station, and aA phase electrical connection.

delay device in said` i 9. In a Vmultiplex telegraph system, a control station having a transmitter, a controlled station having a transmitter and a receiver, channelconnecting distributors for said transmitters and receiver, means for operating the distributor for saidv control station and the-distributor for said receiver at speeds bearing. a constant ratio vto each other and means electrically operated by the receiving distributor for driving the transmitting distributor of said controlled station at a speed bearing a constant ratio to the speed oi' ratio to each other, and means electrically operated by the distributor of the receiver of one station for driving the distributor of the transmitter of that station at a speed bearing Aa constant ratio thereto.

, l1. In a multiplex telegraph system, two transmitters and two receivers, a plurality of message channels for each transmitter and for each receiver, a distributor for each transmitter and each receiver for connecting its message-channels in succession thereto, means for operating the distributor of one transmitter and the distributor of one receiver at speeds bearing a constant r'atio to each other, means for operating the distributor of the other transmitter and the other receiver at speeds bearing a constant ratio to each other, means operated by the distributor of one receiver for producing a pulsating voltage and a motor operated from said voltage for driving the distributor of one of said transmitters at a speed bearing a constant ratio thereto.

12. In a multiplex telegraph system, two stations each having a transmitter and a receiver, a plurality of message-channels for each transmitter, a distributor for connecting the messagechannels of each transmitter in succession thereto, a plurality of message-channels for each receiver, a distributor for connecting the messagechannels of each receiver in succession thereto, means for operating the distributor of a transmitter of each station and that of the receiver of the other station at speeds bearing a constant ratio to each other, meansvelectricallykoperated by the distributor of the receiver of .one station for driving the distributor of the transmitter of that station at a speed bearing a constant ratio thereto and mean-s to adjust the phase of the sig-- nals arriving from the last mentioned transmitter to coincide with that of thedistributor of the other transmitter.

13. In a multiplex telegraph systemtwo transmitters and two receivers, a plurality of messagechannels for each transmitter and for each receiver, a distributor for each transmitter and each receiver for connecting its message-channels in succession thereto, means for operating the distributor of one transmitter and one receiver at speeds bearing a constant ratio to each f other, means for operating the distributor of the other transmitter and the other receiver at speeds bearing a constant ratio to each other, means operated by the distributor of one receiver for producing a pulsating voltage, a motor operated from said voltage for driving the distributor of one of said transmitters at a speed bearing a constant ratio thereto, and means to adjust the phase of the signals arriving at one receiver from one transmitter to coincide with that of the distributor of the other transmitter.

14. In a multiplex telegraph system, a control station having a transmitter, a controlled station having a transmitter and a receiver, channelconnecting distributors for said transmitters and receiver, means for operating the distributor for said control station and the distributor for said receiver at speeds Abearing a constant ratiov to each other, a generator of alternating current operated by the receiving distributor and a synsaid controlled station.

15. In a multiplex telegraph system, two stations each having a transmitter and a receiver, a plurality of message-channels for each transmitter, a distributor for connecting the messagechannels of each transmitter in succession thereto, a plurality of message-channels for each receiver, a distributor for connecting the messagechannels of each receiver in succession thereto,

means for operating the distributor of a re-A ceiver of each station and the'transmitter of the other stations at speeds bearing a constant ratio to each other, a generator of alternating current operated by the distributor of the receiver of one station and a synchronous motor energized by said generator for driving the distributor of the transmitter of that station.

16. In a multiplex telegraph system, two transmitters and two receivers, a plurality of messagechannels for each transmitter and for each receiver, a distributor for each Itransmitter and each receiver for connecting its message-channels in succession thereto, means for operating the distributor of one transmitter and one receiver at speeds bearing a constant ratio to each other, means for operating the distributor of the other transmitter and the other receiver at speeds bearing a constant ratio to each other, a generator of alternating current operated by the distributor of one receiver and a synchronous motor energized by said generator for driving the distributor of one of said transmitters.

17. In a multiplex telegraph system, two transmitters and two receivers, a plurality of messagechannels for each transmitter and for each receiver, a distributor for each transmitter and each receiver for connecting its message-channels in succession theretof, means for operating the distributor of one transmitter and one receiver at speeds bearing a constant ratio to each other, means yfor Aoperating the distributorof the other transmitter and the other receiver at speeds bearing a 'constant ratio to each other, a generator of alternating current operated by the distributor of one receiver, a synchronous motor energized by said generator for driving the diS- tributor of one of said transmitters and means to adjust the phase'of the signals arriving from one transmitter to coincide with that of the distributor of the other transmitter.

18. In a multiplex telegraph system,l two stations each having a transmitter and a receiver, aplurality of message-channels for each transmitter, a distributor for connecting the messagechannels of each transmitter in succession thereto, a plurality of message-channels for each receiver, a distributor for connecting the messagechannels of each receiver in succession thereto, means for operating the distributors of a transmitter of each station and the receiver of the i other station at speeds bearing a constant ratio to each other, a generator of alternating current operated by. the distributor of the receiver of one station,a` synchronous motor energized by said generator for driving the distributor of the transmitter of that station and means to adjust the phase of the signals arriving from. the last mentioned transmitterto coincide with that of the distributor of the other transmitter.

RICHARD E. MATHES. 

